1. Field of the Invention
The present invention generally relates to techniques using hydrogen peroxide released from hydrogen peroxide complexes for sterilizing articles such as medical instruments and materials.
2. Description of the Related Art
Modern medical and dental practices require the use of aseptic materials and devices, i.e., the materials and devices must be generally free from germs, bacteria, etc., and many of these devices are meant for repeated use. However, in order to achieve this asepsis, efficient sterilization processes are needed for treatment of reusable materials and devices. These processes are needed not only at hospitals and dental offices, but also at the manufacturers of these materials and devices.
Medical instruments have traditionally been sterilized using either heat, as is provided by steam, or a chemical, such as formaldehyde or ethylene-oxide gas or vapor state. Each of these methods has drawbacks. Many medical devices, such as fiber optic devices, endoscopes, power tools, etc., are sensitive to heat, moisture, or both. Formaldehyde and ethylene oxide are both toxic gases that pose a potential hazard to health care workers. Problems with ethylene oxide are particularly severe, because its use requires long aeration times to remove the gas from articles that have been sterilized. This makes the sterilization cycle time undesirably long. In addition, both formaldehyde and ethylene oxide require the presence of a substantial amount of moisture in the system. Thus, the device to be sterilized must be humidified before the chemical is introduced or the chemical and moisture are introduced simultaneously. Moisture plays a role in sterilization with a variety of other chemicals in the gas or vapor state, in addition to ethylene oxide or formaldehyde.
Sterilization using hydrogen peroxide vapor has been shown to have some advantages over other chemical sterilization processes, and the combination of hydrogen peroxide with plasma provides additional advantages. Hydrogen peroxide vapor can be generated from aqueous hydrogen peroxide solutions or from solid hydrogen peroxide complexes. However, the use of hydrogen peroxide in aqueous solutions of hydrogen peroxide to generate hydrogen peroxide vapor for sterilization may cause problems. At higher pressures, such as atmospheric pressure, excess water in the system can cause condensation. Thus, the relative humidity in the sterilization enclosure must be reduced before introducing the aqueous hydrogen peroxide vapor.
The sterilization of articles containing diffusion-restricted areas, such as long narrow lumens, presents a special challenge for hydrogen peroxide vapor that has been generated from an aqueous solution of hydrogen peroxide. The first problem arises because water has a higher vapor pressure than hydrogen peroxide and will vaporize faster than hydrogen peroxide from an aqueous solution. Another problem is that water has a lower molecular weight than hydrogen peroxide and will diffuse faster than hydrogen peroxide in the vapor state. Therefore, when an aqueous solution of hydrogen peroxide is vaporized, the water reaches the items to be sterilized first in a higher concentration. The water vapor, therefore, becomes a barrier to the penetration of hydrogen peroxide vapor into diffusion restricted areas, such as small crevices and long narrow lumens.
This problem cannot be solved by removing water from the aqueous solution and using more concentrated hydrogen peroxide, since concentrated solutions of hydrogen peroxide, i.e., greater than 65% by weight, can be hazardous due to the oxidizing nature of the solution. The shortcomings of aqueous hydrogen peroxide sterilizers of the prior art are overcome by using a non-aqueous source of hydrogen peroxide which releases a non-aqueous hydrogen peroxide vapor. In these processes, a solid peroxide complex is heated in a vaporizer and the vapor is diffused into the sterilization chamber.